Drug-eluting implantable medical devices have become popular in recent times for their ability to perform their primary function (such as structural support) and their ability to medically treat the area in which they are implanted.
For example, drug-eluting stents have been used to prevent restenosis in coronary arteries. Drug-eluting stents may administer therapeutic agents such as anti-inflammatory compounds that block local invasion/activation of monocytes, thus preventing the secretion of growth factors that may trigger VSMC proliferation and migration. Other potentially anti-restenotic compounds include antiproliferative agents, such as chemotherapeutics, which include rapamycin and paclitaxel. Other classes of drugs such as anti-thrombotics, anti-oxidants, platelet aggregation inhibitors and cytostatic agents have also been suggested for anti-restenotic use.
Drug-eluting medical stents may be coated with a polymeric material which, in turn, is impregnated with a drug or a combination of drugs. Once the stent is implanted at a target location, the drug is released from the polymer for treatment of the local tissues. The drug is released by a process of diffusion through the polymer layer for biostable polymers, and/or as the polymer material degrades for biodegradable polymers.
Controlling the rate of elution of a drug from the drug impregnated polymeric material is generally based on the properties of the polymer material. However, at the conclusion of the elution process, the remaining polymer material in some instances has been linked to an adverse reaction with the vessel, possibly causing a small but dangerous clot to form. Further, drug impregnated polymer coatings on exposed surfaces of medical devices may flake off or otherwise be damaged during delivery, thereby preventing the drug from reaching the target site. Still further, drug impregnated polymer coatings are limited in the quantity of the drug to be delivered by the amount of a drug that the polymer coating can carry and the size of the medical devices. Controlling the rate of elution using polymer coatings is also difficult.
Bare metal, uncoated drug-eluting stents made from a hollow-tubular wire filled with a therapeutic material have been proposed. However, forming a hollow-wire stent by bending a hollow-wire into a stent form may cause kinking, cracking, or other undesirable properties in the finished stent. Accordingly, bare metal, uncoated drug-eluting stents are needed that utilize the advantages of a hollow-wire stent, such as the ability to delivery increased quantities of the therapeutic substance and improved control of the elution rate of the therapeutic substance, while reducing potential manufacturing difficulties of a hollow-wire stent.